1. Field of the Invention
The present invention relates to a mixer circuit used for a large scale integration (LSI) for radio communications.
2. Background Art
In radio communications of the prior art, mixer circuits for frequency converting radio frequency (RF) signals have been used.
As technology scaling arises with the development of CMOS process technology, a reduction in power supply voltage has become a serious problem in the design of future RF analog circuits. Further, since RF analog circuits have been increasingly mounted in portable equipment, another significant challenge is to operate LSIs for radio communications, on which RF analog circuits are mounted, with low power.
However, the mixer circuits used for LSIs according to the prior art have been mainly made up of MOS transistors stacked in two stages or more, so that the mixer circuits of the prior art are not suitable for low-voltage operations.
In order to solve this problem, mixer circuits for low-voltage operations (a circuit of a mixer core and an adding circuit of analog signals) have been proposed (for example, see Japanese Patent No. 3520175).
In order to achieve a mixer circuit with this circuit configuration, however, an adding circuit of analog signals is necessary.
When analog signals are added by the adding circuit, power is consumed because of the DC bias currents of MOS transistors.
Thus it is difficult for the mixer circuit of the prior art to have a low-power adding circuit, though the mixer circuit can achieve low-voltage operations.